The present invention relates to a plating method and a plating apparatus, a program for electric plating using the method and a recording medium for storing the program, as well as a manufacturing method and a manufacturing apparatus for semiconductor devices.
In recent years, an improvement in device operation speed has been demanded for attaining a higher degree of integration and higher function of semiconductor devices. However, an increase in the operation speed is more limited due to delay time of wiring as the device operation speed increases. In view of the above, it has been intended to improve the operation speed by decreasing the dielectric constant of interlayer insulation films to suppress inter-wiring capacitance and using wiring materials of low resistance to decrease wiring resistance.
For this purpose, it has been studied to form wirings by a damascene method using copper with a specific resistivity of as low as 1.7 μΩcm. Unlike formation of aluminum wirings, etc. by the existent sputtering method, the damascene method bores grooves or holes for wiring at first and then buries copper by electric plating into the grooves or holes to form wirings. For application of electric plating, conductive films are necessary so that a portion where the electric plating is applied can be made conductive. The conductive film is usually formed by depositing a copper film by a sputtering method. However, since copper itself is liable to be oxidized and not forms a passivation film, oxidation proceeds easily when it is exposed to atmospheric air.
On the other hand, electric plating to a wafer having a conductive film is usually applied by a batchwise treatment of discharging and supplying a plating solution for each plating treatment. In a cup type plating apparatus, a wafer as a cathode electrode is located at the upper end of a plating vessel and an anode electrode is located at a lower portion of the plating vessel being opposed to the cathode electrode. Accordingly, the wafer having the conductive film is in contact with a plating solution at the same time as the plating solution is filled in the plating vessel. Then, it is necessary to avoid uneven plating, for example, by keeping a wafer in a plating solution without applying electric plating for a certain period of time till the wafer is wetted sufficiently with the plating solution and bubbles on the surface are eliminated.
However, a copper plating solution is generally a copper sulfate solution containing sulfuric acid, which is a strongly acidic solution at a pH of 1 to 4. When a wafer having a surface oxidized conductive film is immersed in such an aqueous acidic solution without applying a voltage, copper oxide on the surface is dissolved easily.
Further, when nickel, cobalt, nickel alloy or cobalt alloy having a higher ionization tendency than that of copper is used for the conductive film and an underlying conductive film 47 formed by way of a barrier film 48 on the surface of an insulation film 46 is dissolved easily, as shown in FIG. 20A. In a case where the step coverage of the conductive film 47 is small, the conductive film is leached out locally at a portion where the film thickness is thin and, when electric plating is applied, the obtained copper plated film 49 possibly becomes uneven or incomplete to sometimes leave a void 50 in the film 49 as shown in FIG. 20B.
The thickness of the conductive film tends to be reduced on the wall surface of fine grooves or holes bored on the surface of the semiconductor wafer as compared with wafer surface. In a semiconductor device having a conductive film as extremely thin as 1 nm to 50 nm, since it is expected that the device will be further refined, it is conceivable that the thickness for the underlying conductive film will be further reduced. In such a super thin film, leaching of a conductive film or an oxide thereof, even little, results in ununiform thicknesses or local defects of the conductive film. Consequently, this causes unevenness of the thickness of the plated film, disconnection, voids or the like.
Then, to suppress the dissolution of the conductive film, Japanese Patent Laid-open No. 10-152799, for example, proposes an electric plating apparatus in which a positive electrode and a negative electrode are faced to each other in a plating vessel, an auxiliary negative electrode is located near the negative electrode and a plating power source is provided, wherein electric current is supplied from the auxiliary negative electrode to the negative electrode for a period of time in which a plating solution is not filled between the negative electrode and the positive electrode thereby substantially eliminating the dissolution of the underlying film of the negative electrode due to the plating solution. In this method, since the current is applied between the auxiliary negative electrode as a counter electrode and the negative electrode, dissolution of the conductive film is suppressed after both of the plated body as the negative electrode and the auxiliary negative electrode come in contact with the plating solution to be brought into electrical conduction.
In this case, when the current is applied, the auxiliary negative electrode acts as an anode electrode while the negative electrode acts as a cathode electrode. As a result, the plated body comes in contact with the plating solution for a certain period of time until both of the negative electrode and the auxiliary negative electrode are wetted with the plating solution, with no suppression for the dissolution of the conductive film, so that an oxide film formed on the surface of the conductive film is partially dissolved. Therefore, this increases unevenness of the underlying film.
To suppress the dissolution of the conductive film at the instant the plated body comes in contact with the plating solution, current has to be supplied at the instance the plated body comes in contact with the plating solution. However, the dip timing of the wafer surface to the plating solution is not uniform. In a usual cup type plating apparatus, since the plating solution is introduced from an inlet at the lower center of a plating vessel as a jet stream into the plating vessel, the surface of the plating solution is raised more in the central portion of the plating vessel as compared with the vicinity of the wall surface of the plating vessel, so that the wafer is wetted from the central portion with the plating solution. For example, in a case where a current is supplied at the instance a portion of the plated body comes in contact with the plating solution, since the current is concentrated only to a portion in contact with the plating solution, electric plating is started locally to increase variations in the film thickness.
Further, while a voltage may be previously applied prior to the contact of the plated body with the plating solution so that a minute current flows when the plated body comes in contact with the plating solution. However, when a portion of the plated body comes in contact with the plating solution to enable electric conduction with the auxiliary electrode, since the current is concentrated also in this case to a local region wetted with the plating solution, a current enough to proceed plating flows, making it difficult to obtain a uniform plated film.